A switching power supply device having a combination of a power factor correction converter and a DC/DC converter is described in, for example, JP-A-2014-131455. This switching power supply device has a load state detection unit for detecting a state of a load in the DC/DC converter. When the load state detection unit detects that the state of the load in the DC/DC converter is a light load state, the DC/DC converter transmits a light load detection signal to the power factor correction converter, and the power factor correction converter decreases frequency. As a result, efficiency in a light load state can be improved.